It’s part of the setting. The scenery. Like the empires. We all know there aren’t any real empires full of people. They’re just a fiction that is the setting of the game. They have some game mechanics attached – standings, Factional Warfare, damage types – but mostly they are irrelevant. There are very few forum posts complaining about empires.
Security ratings are like that. They’re mostly a fiction, but they’re attached to a mechanic which affects the cost of combat in different places in space, giving variety.
The problem is that players mistake the fictional setting for some sort of moral or gameplay guarantee or intention. Gankers and pirates are breaking the in-game fictional law. Therefore (a) the game needs fixing because it isn’t enforcing it’s fictional in-game law perfectly and (b) the people playing pirates are bad people (“bullies”). This confusion seems to happen all the time!
Or maybe nobody is confused and they’re metagamers trying to win by changing the rules to suit themselves, which is to say cheats.
Imagine if highsec were called you-lose-your-ship-if-you-attack sec?